Adjustable attenuators for microwave radio energy



I959 KIYO TOMIYASU 2,907,961

ADJUSTABLE ATTENUATORS FOR MICROWAVE RADiO ENERGY Filed Sept. 14. 1954 INVENTOR h IYO Tom/msu absorption and power breakdown.

ADJUSTABLE ATTENUATORS FOR MICROWAVE a. VRADIOYENIERGY' Tomiyasu, Flushing, N.Y., assignor to Sperry Rand Corporation, a corporation of Delaware Application September 14,1954, Serial No. 455,827

' ,4 Claims. 01. 333-81) This invention relates to improvements in adjustable.

levels such as are encountered in the operation and testing of high power radar systems and their components.

- Heretofore generally it has been sufiicientto test theoperation of microwave systems and components at reduced power levels since there was no doubt of the ability of the system to handle much higher powers than those to be used. More recently, however, many microwave systems are intended to be used at power levels attenuators for microwave radio energy, and particularly to attenuators for operation at relatively high power energy incident upon it. The material of the body 4.

near the maximunr capacities of some of their wave guide components; Therefore the system must be tested in operation at its full rated power to check for power I Such high power tests require among other things, adjustable attenuators capable of carrying and absorbing high power without breakdown or other deleterious effects.

Accordingly, it is the principal object of this inven- ,tionto provide improved adjustable attenuators of high power handling capability.

Another object is to provide adjustable high power attenuators that are simple in construction and reliable in operation. I

further object is to provide attenuators of the described type that can be accurately calibrated, and will retain theiraccuracy under the intended operating jconditijons I f- ..a notlier object is to provide high power adjustable nuators" that can be designed to introduce'little or negligible reflections inwave guide systems to which they are connected.

Still another object is to provide attenuators wherein the power dissipation takes place in a body of lossy material outside the wave guide, where the resulting heat may be radiated or otherwise carried away readily.

A further object is to provide attenuators of the fore going type with means for minimizing or preventing the leakage of microwave radio energy from the attenuator structure.

Another object is to provide a high power adjustable attenuator capable of producing a minimum attenua tion of substantially zero.

According to the present invention, the foregoing ob jects are achieved by providing a hollow conductive wave guide with an opening in one of its wall portions and placing a body of microwave energy absorbing material adjacent the opening, outside the guide. The attenuation is varied by varying the area of absorbing material that is exposed to the interior of the guide. This may be done by varying the effective area of the opening, as by means of a movable conductive shutter interposed between the body of absorbing material and the opening.

The invention will be described with reference to the accompanying drawing, wherein:

Fig. 1 is a perspective view of an adjustable attenuator embodying the invention,

. Patented ocnie, 1959 "ice ' Fig. 2 is a side elevation, partly in section, of the structure of Fig. 1, and Fig. 3 is a transverse section of the device, taken in the plane 33 of Fig. 2. a v

The main body of the attenuator structure consists of a length of wave guide '1, adapted to be connected between input and output-wave guides or other devices,

not shown, between whichfmicrowave energy is to be transferred with an adjustable amount of attenuation; An opening 2 is provided in one of the wall portions of the guidelz In this instance the opening 2 is'in one of the narrow walls of the guide, is transversely coextensive therewith, and has a substantially greater-extent longitudinally of the guide. The opening 2 is substantially coveredby a body 4 of lossy material, i.e; material that absorbs and dissipates a large portion of any microwave lower guide means 11 and 12 for supporting a flat metal sheet or shutter for motion longitudinally of the wave guide 1. 1

Inside the portions9 and10 of: the housing 7, a series of conductive tin'es15 are provided, extending-outwardly from the upper and lower edges of the opening 2 par allel to'and closely adjacent the plane of the shutter 13. The tines 15 are spaced at small intervals longitudinally of the guide, and are approximately-one quarter wavelength long at the design frequency ofthe device.

The shutter 13 is secured -at "oneof "its ends to' "a suitable'translating means' such' as "a screw '17 arranged to coop'ei-ate'with a'rotatable mit 19 confined between two lugs 21 onthe waveguide A pointer 23 or equivalent fiducial device isconnected to the; shutter 13; for cooperation with a scale 25 which maybe engrave'dlon the adjacent wall of the-waveguide. Y v r The operation of theidescribed device, when the shut:- ter is in the position shown in Figs. 1 and 2, is substantially the same as that of an ordinary wave guide without any attenuating means.

rangement is preferred at present, it will be apparent without further illustration that the lossy body 4 may be supported on and movable'with the shutter 13 instead of being fixed, by making the member 13 approximately twice as long as the opening 2 to provide two approximately equal areas disposed end to end, one lossy and the other conductive.

Since it would be diflicult mechanically to provide perfect contact between the shutter 13 and the adjacent' edges of the opening 2, a small clearance is provided.

The array of tines 15 cooperates with the adjacent surface portions of the shutter 13 to provide substantially the samev eifect, electrically, as if the shutter 13' -were connected to the edges of the opening.

The shutter 13 closes the 7 opening 2 and functions as a part of the conductive wall leakage, of microwave energy around the shutter and avoids erratic contact effects and frictional forces opposing free motion of the shutter. The housing member 5 cooperates with the tines where they are exposed to it, to minimize leakage when the shutter is partially or totally withdrawn from the opening. It also functions as a shield tofurther reduce leakage and prevent radiation which might otherwise disturb the operation of nearby apparatus.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing, from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted asillustrative and not in a limiting sense.

What is claimed is: v

1. Apparatus for adjustably attenuating microwave radio energy, comprising a hollow conductive wave guide having a wall portion provided with an opening, means outside said wave guide and covering said opening, said means including a body of lossy material and a sheet of conductive-material, means supporting said sheet of conductive material for movement with respect to said opening to vary the area of said lossy material that is exposed to the interior of said wave guide, and a plurality of conductive tines connected to said waveguide adjacent said opening and extending substantially parallel to said conductive sheet and outwardly from said opening, said tines cooperating with said sheet to prevent the escape of microwave energy through the space between said sheet and said tines. Y

2. Apparatus for adjustably attenuating microwave radio energy, comprising a hollow conductive Wave guide having a wall portion provided with an opening, a body of lossy material outside said wave guide and covering said opening, and a sheet of conductive material, means supporting said sheet of conductive material for movement between said body of lossy material and said opening to vary the area of said lossy material that is exposed to the interior of said wave guide, and a plurality of conductive tines connected to said wall portion adjacent said opening extending substantially parallel to said conductive sheet and outwardly from said opening, said tines cooperating with said sheets to prevent the escape of microwave energy through the space between said sheet and said tines.

3. An adjustable attenuator for microwave radio energy, comprising a hollow wave guide having a wall portion provided with an opening, the transverse extent of said opening being substantially less than the perimeter of said wave guide, a body of lossy material having a surface substantially coextensive with said opening and means supporting said body outside said wave guide adjacent said opening, a metallic shutter outside said wave guide adjacent said wall, said shutter being substantially wider than said opening, means supporting said shutter for motion longitudinally of said wave guide and over said opening to vary the area of said lossy material that is exposed to the interior of said wave guide, and a plurality of conductive tines connected to said wall adjacent said opening, said tines extending parallel to said shutter, substantially perpendicular to the longitudinal axis of said wave guide, and outwardly from said opening to prevent the escape of microwave energy between said shutter and said tines.

4. An adjustable attenuator for microwave radio energy, comprising a hollow rectangular wave guide provided with an opening extending longitudinally in one of its narrow walls and extending from one broad wall to the other broad wall, a body of lossy material having a surface substantially coextensive with said opening and means supporting said body outside said Wave guide in a position such that said surface substantially covers said opening, a metallic shutter outside said wave guide adjacent said narrow wall, said shutter being substantially wider than said narrow wall and extending beyond both edges of said narrow wall, means supporting said shutter for motion longitudinally of said wave guide between said opening and said surface of said body of lossy material to vary the area of said lossy material that is exposed to the interior of said wave guide, and a plurality of conductive tines on said broad walls adjacent said opening, said tines extending substantially perpendicular to said broad walls, parallel to said shutter and outwardly from said opening to prevent the escape of microwave energy between said shutter and said tines.

References Cited in the file of this patent UNITED STATES PATENTS 

